The objective of this study was to investigate selenium toxicosis in larval northern pike (Esox lucius) originating from reproductively mature pike collected downstream of a uranium milling operation in northern Saskatchewan, Canada. Eggs were obtained from female pike collected from a reference site and three sites representing an exposure gradient (approximately 2, 10, and 15 km downstream of effluent discharge). Embryos were incubated following a two-way (crossover) analysis of variance experimental design that allowed discrimination between effects due to maternal transfer to eggs and effects due to site water exposure in the developing embryos. The major finding of this study was a significant increase in the frequencies of individual deformities (skeletal curvatures, craniofacial deformities, and fin deformities) and edema in fry originating from high and medium exposure site females (mean selenium concentrations of 48.23 and 31.28 microg/g egg dry weight and 38.27 and 16.58 microg/g muscle dry weight, respectively) compared to reference site females. Selenium concentrations resulting in a 20% increase in total deformities above background levels (EC20S) were 33.55 and 21.54 micro/g dry weight in eggs and muscle, respectively. Mathematical conversion of the egg- and muscle-derived relationships to whole body selenium levels resulted in similar EC20S of 15.56 and 17.72 microg/g dry weight, respectively. These relationships between tissue selenium levels and larval deformities suggest that northern pike are within the same range of sensitivity to selenium as the majority of warm water (e.g., centrarchids and cyprinids) and cold water (e.g., salmonids) fish species studied to date.

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Selenium (Se) is a developmental toxicant in oviparous vertebrates. The adverse reproductive effects of Se toxicity have been predominantly investigated in fishes and birds with only a few studies focusing on amphibians. The objective of this study was to determine tissue-based toxicity thresholds for early life stage Se toxicities in Xenopus laevis as a consequence of in ovo exposure through maternal transfer of dietary Se. Following a 68-day dietary exposure to food augmented with l-selenomethionine (SeMet) at measured concentrations of 0.7 (control), 10.9, 30.4, or 94.2 μg Se/g dry mass (d.m.), adult female X. laevis were bred with untreated males, and resulting embryos were incubated until 5 days postfertilization (dpf). The measured Se concentrations in eggs were 1.6, 10.8, 28.1, and 81.7 μg Se/g d.m., respectively. No biologically significant effects were observed on fertilization success, hatchability, or mortality in offspring. Frequency and severity of morphological abnormalities were significantly greater in 5 dpf tadpoles from the highest exposure group when compared to the control, with eye lens abnormalities being the most prominent of all abnormalities. The estimated EC10 value for frequency of total early life stage abnormalities was 44.9 μg Se/g egg d.m., which suggests that this amphibian species is less sensitive to in ovo Se exposure than most of the fish species studied to date.